I don't acidify my water for blueberries. I use canal water, which I am sure is quite high in pH (need to measure it some time). I just periodically sample the soil and when the pH starts creeping up I give them a *little* sulfur. My pH doesn't creep up too fast but mine are in the ground, so maybe there is greater pH buffering than if they were in pots. I keep them mulched with leaves and grass clippings and I've found that even around pH 6 they are healthy. I've actually done more harm by lowering the pH too low.

What I forgot to mention is that some of the pots that now test 4.4 to 6, tested about 2.5 to 3 a couple months ago. I raised the pH of those using well water. So this is the second time in a couple months of excessively low pH.

That leads me to think that I'm lowering pH of the well water too low.

backyardener:

Canal water, if from snow melt, is probably not high in carbonates like well water. But I agree that bb at pH 6 can grow just fine.

Can anyone explain how watering with pH 5 water can lower media pH below 3? I know enough to think it's possible but could use an explanation.

Thank you!!

There may be bacteria in the soil eating the sulphur you are adding that is driving the pH down. I know that the reason powdered sulphur lowers pH is due to the bacteria eating the sulphur, not the acidity of powdered sulphur, and sulphuric acid contains sulphur. So, you may want to aim to lower the water to only pH 6 with the sulphuric acid. pH is complex chemistry and there can be many factors involved. I got a too-low reading of 3 recently on some of my plants, I think it was because they had not gotten much water recently and so there was more acidic chemicals in the soil to go into solution because the soil had not been flushed out.

Scott

Dont tell me that fruitnut, I thought you were the man??? I guess I need to check my soil ph as well. Can I raise my potted plants and catch the water coming out of the bottom of my plant to get the media ph?

The canal water is from snow melt, but it travels to my house via canals lined in some places with concrete and comes in contact with our naturally alkaline soil, so I only assumed it was alkaline by nature. I'm going to measure it now because I am very curious.

I have a thought about your puzzling situation. Are you certain that your water pH is 5? I thought your Accurate 8 pH meter was not made to measure a liquid. How are you measuring the pH of the water, is it possible you are over acidifying? As Scott said, pH chemistry is quite complex (and it has been a while since I've studied it). I do know that you cannot mix equal parts of acid with pH 2 with water of pH 8 and expect a solution of pH 5.

Also, I'm not sure how the hydrogen ions from your acidified water will interact with the soil. It seems possible to me that if you keep adding acidified water (keep adding hydrogen ions) that the pH could drop below the pH of the water - as you have observed. Think of naturally acidic soil... it reaches pH lower than the rain water that falls on it. I'm no soil or chemistry expert, it's just an idea.

BlueBoy, I think your method will work reasonably well if you water with distilled water and and collect the water running out. If you do not use distilled water, the result will be skewed by the water that you use. My method is similar, I put a sample of media in distilled water, mix well, then measure the pH of the water after the media settles to the bottom of the container.

Scott:

With enough experience we'll get this figured out. I'm moving up to pH 6 and see how that goes.

blueboy:

I'm trying to make all the mistakes so everyone else doesn't have to, at least that's my excuse. Yes you'd better figure out how to measure media pH. I can't say about checking drainage water. But I still trust the Accurate 8 and will try to go from there.

I'll attempt an explanation about how pH 5 water could lower media below 5. By acidifying to 5 we're left with a solution that has free sulfuric acid. So that solution has a fairly high concentration of free negatively charged SO4 ions. As those pass through the media every day or two they continue to strip out the Ca+ and Mg+ forming gypsum and MgSO4. This drops the pH lower and lower.

When you use rainwater it maintains the original balance of soil chemistry. We might need to only lower pH of well water to 7.

What I should have said is that by watering with distilled water you would/maybe/might maintain the original chemistry of the media. Rainwater can have much different chemistry depending on where it originates. Some is as acid as my pH 5 acidified well water.

I found a link from the Aggi Ag. that recommends acidifying alkaline water to 5.5 to 6.5ph for plant nutrient up take

Your well water is acidic? Always assumed most wells were very basic. I really need to check mine. My blueberries look great and I've been watering with well water. I use a peat moss/wood chip mix. Although I get 20-30 inches of rain from spring to fall, so that may keep it low.

blueboy:

I think the link below is what you are referring to. So acidifying to 6 might indeed be good. I think my experience says 5 is too low.

Lets work on this and report back over time as to what we find.

Here is a link that might be useful: Aggie link

I'm not a chemist, so what I say may very well be incorrect. Here is my attempt though. When you water with ph 5 water, some of the acidifying ions will stay in the soil, and overt time, the concentration will be higher, and ph will be lower. Also as water evaporates, the concentration will also be higher. Though ph is log scale, so if the soil is 10x drier, then ph will be reduced by 1?

That also raises a question about how soil ph value is defined? Does it depend on how heavily and recently it's watered?

Fruitnut, I know you get your acid from auto parts store. Do you know whether it's fresh or recycled/reprocessed? Since auto batteries contain a lot of lead, even reprocessed acid may contain quite some. That's something you may want to find out.

tc:

Don't know the answer to your question about lead but will try to find out. What I really need to do is put in a bigger rainwater collection system. I'm at 300 gal right now and need one or two of those 1550 gallon tanks. Two inches of rain off the greenhouse would give me 3100 gallons if I had two tanks. Right now I'm using about 80 gal a week for potted blueberry.

Just bought a General Hydroponics pH test kit about $8. It might be better than the indicator strips for water solutions. The Accurate 8 is for soil media only.

I dont know if you have spent any time over on the container forum. Al "tapla" Is one of the most knowledgeable people on growing anything in containers. Hehelped me with my blueberris in pots. He was a big help. They did and are doing very well. filix.http://forums2.gardenweb.com/forums/load/contain/msg101347031585.html

I used to work in the printed circuits industry, and I had to use a pH meter daily, to monitor a machine used for etching printed circuit boards. So, over time, I got pretty good at calibrating pH meters, and using them to get results that were accurate to about 0.05, plus or minus. The industrial or lab meters are fairly expensive, but I used to own a Hannah Instruments pH checker that only cost around 45 dollars. It lasted three years, which is pretty good for the pH electrode. However, I was aware of certain dye indicators that can be used to check pH, and now I use bromocresol green for checking blueberry soil pH. This solution covers the range 3.8 to 5.4, so it works well for blueberries. I collect about a table spoon of dirt, mix it with an equal amount of DI water(or distilled water) to make a slurry, and filter the slurry through a paper coffee filter. When I have a few drops of filtrate, half a teaspoon is plenty, then I add some bromocresol green, and observe the color. Yellow indicates pH = 3.8, or below. Blue indicates 5.4, or above, and some shade of green indicates the pH is between 3.8 and 5.4. So I can't get the same precision possible with a calibrated pH meter, but I am very confident of the results I do get. I have compared results with bromocresol green and a calibrated pH meter, and the two methods agree. If your blueberry shrubs are green and they look healthy, I would consider the condition of the leaves to be a reliable indication that pH is within acceptable range. In that situation, I would be reluctant to make any significant changes in how the shrubs are cared for. With regard to shrubs in pots, if you asked me to check the pH, I would pour about a gallon of DI water into the pot, and collect the filtrate at the bottom of the pot, to be tested. No doubt that adding a gallon of DI water would lower pH slightly, so the result would be off a small amount. However, I think the result would be within 0.5 unit. I hope this helps.

There are thousands of sand aquifer wells here with pH ~4.5. There are many with pH even slightly lower, 4.3-4.1. Dissolved CO2 (carbonic acid) can only drive pH down to ~4.5 so the lower pH shows some mineral acidity. Many of the wells with lower pH show elevated nitrate, which has to come from the surface. Many ultimate sources of nitrate are organic and go through an ammonia (or ammonium) stage in breaking down, and ammonia is widely used directly in agriculture now. OK, to the important part: when bacteria convert ammonia to nitrate (nitrification) the reaction releases acidity. In a poorly buffered and already acidic system, it can notably drive pH down, even in a huge natural system.

I don't think applied sulfate per se drives down pH, but applied sulfur surely dies, apparently by biologically producing sulfurous acid (and ultimately somehow sulfuric acid).

Still, your pH readings were mighty low.

I don't have the chemistry background that many of you do or the experience growing blueberries. Nevertheless, I can say that after three years in pots my plants are thriving and the entire time I have been watering with water that has a pH of about 7. It seems to me that if I was going to see a problem with the pH as a result of the water I would have seen it by now.

My plants are in fir bark and peat and I add sulfur each year and fertilize with ammonium sulfate or Miracle Grow for acid loving plants.

It may be eaisier to just replace the soil every so often during the dormant period than it would be to add acid with each watering. The addition of sulfur, topdressing with peat, and use of acid fertilizers such as ammonium sulfate should keep the soil in an acceptable pH range..........it has for me for three years now.

RM

RM:

You may be right but my well water and lots elsewhere has an awful lot of carbonates. It's a lot different than snowmelt or river water. I can raise the pH from 3 to 5 in a matter of an hour. I've done it and will with the ones in question. But I'll stop at 4 to 4.5.

Fruitnut,

Just trying to help.....I wonder, is it possible that your meter is taking a reading on the water you have just added rather than the soil? A 100 fold alkaline increase in one hour seems unlikely with one addition of water.

RM

RM:

I've had to raise pH twice now going on three times. After raising pH with well water it remained stable several days later. The plants in question look great and are growing nicely.

I checked one of my potted plants by watering it with DI water and collecting the water that drained out of the pot. Measured the ph with a ph tester I borrowed from the lab at work. Dont know what type but I promise its not cheap. Has a short glass probe on it and its made to test liquids. It showed a ph of 5.92. Then mixed some of the soil 2inchs below the mulch with DI water. It showed a ph of 5.53. After that I checked 2 of my raised beds by mixing soil 4inchs below the mulch with DI water. One came back 5.06 and the other 4.91. The soil just under the mulch showed a ph of 3.67. I did add about a 1/2cup of soil sulfer into the top 3inchs about 2 months ago and have been watering with municiple city water acidified to ph5. So far so good;) I will check the rest of them soon.

Blueboy,

The range of PH values you are getting is interesting although not so surprisng.

Fruitnut,

Last night I did some browsing and found this article on turf building that supports what you have been saying about the carbonates:

Here is an exert:

Can acid-forming fertilizers keep the soil pH from getting too high?

Under many circumstances the quantity of bases that is being supplied in the irrigation water far exceeds the quantity of acid formed by addition of fertilizer. Under those conditions acid-forming fertilizer will not control the problem of increasing soil pH. However, where very high rates of acid-forming fertilizer are applied (e.g., 6000 lb ammonium sulfate per acre per year on bermudagrass turf) it is possible to keep soil pH acidic with the fertilizer (Snyder, et al. , Agron. J. 71:603-8). The quantities of bases applied via the irrigation water and the acid-forming potential applied in the fertilizer must be known in order to determine the magnitude of the effects. (end)

I wonder Fruitnut if you could buffer the upward pH trend by using larger pots than you currently are. I am using half wine barrels and they hold a great deal of bark and peat. A larger pot may allow you to use less acid while watering.

RM

6,000 lbs ammonium sulfate per acre!!!! Man that would be some green bermuda grass.

I'm not going to larger pots, too heavy. I have to move things around whether I want to or not at least once or twice a year.

If nothing else, you are making a case for metal probe type pH checkers. The fact that your blueberry shrubs are green and healthy means that you must be getting reasonably accurate pH numbers from your probe read-out. My experience has been that blueberry shrubs will green up and grow in a fairly wide pH range, 3.5 to 6.5. My best guess is that the low pH readings you are seeing are accurate, and that your countermeasure, raising pH with well-water, is appropriate.

Fruitnut,

I understand your interest in being able to move the pots from one place to another without losing a disc in your lower back! You definitely are NOT going to be moving a half wine barrel full of soil very easily. And, hey we are all learning here by going through this process. You have me wanting to buy a new pH meter!

But.........I also think some of the flashiness and rapid ups and downs you are seeing with your pH readings are an indication that your pots are too small. Go to larger pots and more media and I expect you will find moderated pH readings. It makes sense, think about pouring a half gallon of acid treated water on a three gallon pot versus the same treated gallon of water on a 25 gallon pot.

RM

RM:

I'm sure there is something to what you are saying. But I think I'd have to go to in-ground and a more mineral soil to really buffer pH.

My plants are already too big in small pots. Of course I could prune them back but they look so good the way they are. I'll be alright when I can get away from treated well water. It'll rain one day soon...I think.

Just checked the pH again after two waterings with untreated well water. A few spots still test below 3. But more spots test 4 to 4.5. It's going to take a few more waterings but things seem headed in the right direction.

Fruitnut,

I'm confident you will get it figured out one way or another. Blueberries can be a challenge, that's probably why we enjoy growing them so much.

RM

It looks like you've found your answer Fruitnut.

Since there has been some confusion about what pH is, I wanted to add a few comments about it.

I don't remember that much about it myself, but have had discussions with my daughter, and she's pretty brainy on the topic.

It's interesting to me how it works, and this is how I understand it.

pH measures the amount of positively charged H ions/cations. The small "p" stands for the latin term pondus (weight) and the "H" stands for the term Hydrogen (That's why the "p" is always lower case, and the "H" is upper case.)

The reason the pH scale is logarithmic is that a solution with a neutral pH of 7 will have 10 to the minus 7 moles of Hydrogen ions per liter. A solution with pH of 6 will have 10 to the minus 6 moles of Hydrogen ions per liter (10 to the minus 6 being 10 times more than 10 to the minus 7). So as the pH reduces there is a greater and greater concentration of hydrogen ions till you finally get to a theoretical pH of 0, which would be 10 to the zero power, or one. In other words the solution would be more or less 100% hydrogen ions.

Interestingly, there is also a pOH scale which also measures alkaline/acidity and is the inverse of the pH scale. OH is a negatively charged ion/anion. A pOH of 8 would be the equivalent of a pH of 6.

But what's interesting to me is how it comes together. Everyone knows water is H2O. In theoretical terms pure water has a pH of 7 and a pOH of 7. That means there are exactly as many free roaming H+ ions as there are OH- ions (10 to the minus 7 of each), which when come together form H2O.

Sometimes pH probes can be in error because they only measure cations. Hydrogen is not the only cation. Sodium also has a plus one charge and Calcium has a plus 2 charge. The cheaper probes we are talking about will pick up Sodium and Calcium cations in their measurement. You can try it yourself to see if it affects your probe. Take a glass of water from the sink and measure the pH. Then add some table salt to the water and check again. Chances are the probe will indicate a reduction in pH, even though it hasn't really occurred. The probe is picking up the Sodium ions.

I've tried it, and while the error isn't huge, there is some error.

Olpea, that's interesting to read and sounds reasonable.

So on salt, it is NaCl which contains Na+ and Cl- ions. In this case, the pH probe will measure lower than 7 if it measure + ions and pOH probe will measure higher than 7 if it measure - ions, right?

"So on salt, it is NaCl which contains Na+ and Cl- ions. In this case, the pH probe will measure lower than 7 if it measure + ions and pOH probe will measure higher than 7 if it measure - ions, right?"

TC88,

Well I'm not sure about that. A pOH test might only measure hydroxide ions (OH-) but I suppose it depends on the testing equipment.

So while a cheaper pH probe will measure Hydrogen ions, it will also measure other cations and register them as Hydrogen ions, I don't know what testing equipment is used to measure pOH and if that equipment would measure the Chloride anion (Cl-) and register it as an OH- anion.

Please don't ask me any harder questions. I'm already writing past my actual knowledge of chemistry.